Table 1.

Why pursue genetic testing?

Situation	Aim
Diagnostic testing	To establish a genetic diagnosis for an affected patient with no previously established individual or family result.
Confirmation testing	To confirm a genetic diagnosis of an affected patient; this could be Sanger sequencing for a known genetic result of an affected family member or confirmation in an NHS diagnostic laboratory of a result found previously in research.
Carrier testing	To study the genotype for an unaffected family member of a patient with a known pathogenic change. These tests are most commonly performed in family members of patients with an autosomal dominant gene with reduced penetrance, or for women who are at risk of carrying an X-linked disorder.
Predictive testing	To study the genotype for asymptomatic relatives of affected individuals who are at risk of developing the condition themselves. Current UK guidelines are that asymptomatic children under the age of 16 should not undergo predictive testing for an adult onset disorder.
Familial segregation testing	Might be useful for relatives of patients with an autosomal recessive disease, in order to confirm that two pathogenic mutations are in trans.